Separate experiments in which antagonists of prolyl-hydroxylase and each of its cosubstrates/cofactors were supplied to axenic cultures of developing plants of Plagiochila arctica (Hepaticae) had the same result: leaf primordia that are normally suppressed at a very early stage of development continued to develop into full-sized leaves. Since the function of the prolyl-hydroxylase system is the posttranslational conversion of petidyl-proline to peptidyl-hydroxyproline, we tentatively conclude that prolyl- hydroxylase inhibitor-induced desuppression is related to altered synthesis of hydroxyproline-containing proteins (Hyp-proteins). There are two classes of Hyp-proteins widely distributed in green land plants, each with more than one "species" of protein. Both classes are represented in P. arctica, but the number of representatives of each class is not known yet. We propose here: 1. to find out how many Hyp-proteins of each class are synthesized in P. arctica; 2. to more directly test the assumption that the prolyl-hydroxylase inhibitors we used are in fact limiting posttranslational hydroxylation of proline in P. arctica; and 3. to use immunohistochemical procedures to correlate the presence/absence of specific Hyp-proteins identified in P. artica with suppression/desuppression of leaf development. These investigations of suppression/desuppression of cell development bear on several basic biological questions. First, what factors control cell multiplication and cell shape and secondly, what evolutionary role these suppressive effects play in altering phenotypic development? In short, we are seeing the biochemistry whereby phenotype develops from genotype. When suppression occurs during the course of histogenesis, organogenesis or ontogeny largely determines size. Where suppression occurs relative to other developing parts, it largely determines shape. Whether suppression occurs or nor largely determines whether growth and development will be "determinate" vs "indeterminate", or "normal" vs "abnormal" (pathological).